Page 394 - Advanced Organic Chemistry Part B - Reactions & Synthesis

5

Reduction of Carbon-Carbon

Multiple Bonds, Carbonyl

Groups, and Other Functional

Groups

Introduction

The subject of this chapter is reduction reactions that are especially important in
synthesis. Reduction can be accomplished by several broad methods including addition
of hydrogen and/or electrons to a molecule or by removal of oxygen or other electroneg-
ative substituents. The most widely used reducing agents from a synthetic point of
view are molecular hydrogen and hydride derivatives of boron and aluminum, and
these reactions are discussed in Sections 5.1 through 5.3. A smaller group of reactions
transfers hydride from silicon or carbon, and these are the topic of Section 5.4. Certain
reductions involving a free radical mechanism use silanes or stannanes as hydrogen
atom donors, and these reactions are considered in Section 5.5. Other important proce-
dures use metals such as lithium, sodium, or zinc as electron donors. Reduction by
metals can be applied to carbonyl compounds and aromatic rings and can also remove
certain functional groups.

Addition of Hydrogen
H 2 [MH 4 – ] 2 M·
R C X R CH XH R C X R CH XH R C X R 2 CH XH
2
2
2
2
2
2 H +
catalytic hydrogenation
hydride reduction
reduction by metals
X = CR′ O, NR′ X = O, NR′ X = O, NR′
2,
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